A process is described for the removal of volatile radioactive oxides of ruthenium, molybdenum and technetium from the process gases and effluent gases produced during nuclear fuel reprocessing procedures which comprises passing the gaseous stream containing the volatile radioactive ruthenium, molybdenum and/or technetium oxides over a trapping agent selected from the group consisting of alkaline earth compounds, lanthanide compounds and lead oxides at a temperature of from 400.degree. to 1000.degree. C, preferably 500.degree.-700.degree. C which results in the formation of nonvolatile ruthenates, molybdates and/or technetates. The nonvolatile compounds thus formed can be easily handled and kept isolated from the environment during the period of maximum radioactive decay. Alternatively, the trapping agent may be supported.
During the nuclear fission of U.sup.235, ruthenium, molybdenum and technetium are produced as fission products. The ruthenium produced by the nuclear fission process consists of two isotopes, Ru.sup.103 and Ru.sup.106 both of which are radioactive. Together these isotopes produce 6.73 .times. 10.sup.5 Curies of radiation and 3.75 .times. 10.sup.2 watts of energy per metric ton of fuel. Ru.sup.106 has the longer half-life (t1/2 = 1 year) and is involved in a decay series which results in a very energetic beta decay. Considering subsequent released decay energy, the ruthenium present in spent fuel is responsible for approximately two watts/gram of ruthenium. The t1/2 of Ru.sup.106 dictates that any ruthenium recovered during nuclear fuel reprocessing procedures be isolated and retained for approximately 20-30 years. During this time period, the radioactive ruthenium must be prevented from attaining any volatility through high oxidation state oxide formation.
One contemplated method of nuclear fuel reprocessing involves the dissolution of the spent fuel prior to subsequent separation steps. To insure complete dissolution, the materials are subjected to extremely oxidizing conditions. This oxidation, however, would not be elementally specific and hence any oxidizable species in the solution would be oxidized. The radioactive ruthenium and also molybdenum and technetium produced as uranium fission by-products would be subjected to this oxidation step resulting in the generation of RuO.sub.4, MoO.sub.3 and Tc.sub.2 O.sub.7. It is well-known, for example, that RuO.sub.4 has an appreciable vapor pressure over aqueous solutions. The typical quantitative analytical technique used to determine the ruthenium content of a solution involves the distillation of RuO.sub.4 out of an aqueous solution. This same degree of high volatility will be exhibited by the radioactive ruthenium and will consequently pose a serious isolation problem in the reprocessing system.